CARDIFF Council and Environment Agency Wales are to conduct a survey of the otter population this month.

Several of the mammals are thought to inhabit the city's rivers, and they have also been spotted in Cardiff Bay.

The survey will extend to some areas beyond the M4 north of the city. Two otters were killed crossing the motorway in March.

City council ecologist Vaughan Grantham said the safety of the city's otters was one of the main concerns because otters, especially males, are known to cover many miles in a single night.

"We shall be looking at ways of designing culverts, which would allow them to cross under roads rather than over traffic lanes," he said.

"This would be one of the practical environmental benefits of the survey."

Artificial holts for otters to rest and breed would also be considered in some areas.

Otters and their resting and breeding sites are legally protected.

The survey of the mainly nocturnal animals will focus on a search for their spraints (droppings) and will cover water and land areas along the rivers Taff, Ely and Rumney, and smaller tributaries and ponds, where the animals search for food.

Otter populations have been steadily increasing across the UK in recent years, partly because of cleaner rivers. In South Wales there has been a dramatic improvement in many rivers which were once polluted by coal mining and industry.

The otter is listed as a priority species in Cardiff's Local Biodiversity Action, Wild About Cardiff, and it will shortly be the subject of a Species Action Plan to focus conservation work on otters.